How to delete ghost emails in inbox and unread
Since buying and downloading content by iCloud to a new iPhone 6S from an iPad (both are running iOS 11.6.2) the generic Mail app in only the iPhone shows 92 mails in the Home Page icon red dot, but the Inbox and Unread are empty. The previous iPhone 5C did not show this.
When downloading content, the Mail app downloaded over 350 mails, the majority were deleted from the previous iPhone 5C a very long time ago. I settled down to delete the unwanted content of the Inbox, but at 92 shown remaining I ran out of mails to delete from the Inbox.
There are numerous entries in a Google search for this, but none of the fixes that allege to clear this problem work.
How do I clear the remaining unwanted emails and restore the Home page Mail icon to the correct number?
iPhone 6s, iOS 11.2.6